Friedel-Crafts alkylation of aromatics in the presence of Lewis acids are extremely important reactions in both industrial applications and laboratory synthesis. It is generally thought that alkylation reactions proceed by the attack of a carbonium ion formed from the alkylating agent on the aromatic moiety. Common alkylating agents used with Lewis acids are alkyl halides and alkenes. Other aromatic alkylations which proceed through carbonium ion formation use sulfuric acid, toluene sulfonic acids, and sulfonic acids or resins in the strong acid form with alkenes and alcohols to effect aromatic alkylation.
Problems which may be encountered in alkylation reactions with carbonium ions are that the carbonium ion may rearrange and become less reactive and the alkyl aromatic derived from the rearranged carbonium ion may result. Also, in using a Lewis acid such as AlCl.sub.3, the halogen may add to the alkylating agent.
To overcome reactivity problems in alkylation reactions, an excess of alkylating agent is often used. This creates problems in that the recovered residual alkylating agent has lower reactivity than the starting alkylating agent partly due to rearrangement products being formed. Further problems result in Friedel-Crafts alkylation if the alkylating agent is halogenated by the catalyst. The residual alkylating agent may be recovered from the alkylating process. These compounds may be recycled, albeit to form lower yield of alkyl aromatics because of their lower reactivity. They may also be used in other applications such as for fuels. However, depending on the halogen content of the recovered alkylating agents alternate uses may be limited, even for fuel purposes. This could lead to disposal problems including disposal costs for halogenated alkylating agents.